A remotely operated manipulator is used for a work in a place where a person cannot approach, such as a dismantling work of a nuclear reactor. Patent Document 1 discloses a reactor dismantling device for dismantling a structure within a reactor pressure vessel by a remote operation. In this reactor dismantling device, a revolving frame is provided on an auxiliary mount for a work installed in a nuclear reactor, and a telescopic mast having a manipulator is provided at the revolving frame. Further, the telescopic mast is provided with a stabilizer which has a leg stretching to an inner wall surface of the reactor and which prevents a swing of the mast and a reaction force during the work.